The trend towards designing and building fuel efficient, low emission vehicles has increased dramatically over the last decade, this trend driven by concerns over the environment as well as increasing fuel costs. At the forefront of this trend has been the development of hybrid vehicles, vehicles that combine a relatively efficient combustion engine with an electric drive motor.
Currently, most common hybrids utilize a parallel drive system in which power to the wheels is via planetary gears and a transaxle, the power coming from either, or both, a combustion engine and an electric motor. In an alternate hybrid configuration, typically referred to as an integrated motor assist or IMA system, the electric motor is positioned between the combustion engine and the drive system's transmission, the transmission coupling power through the axle to the wheels.
Although hybrids, in general, provide improved fuel efficiency and lower emissions over those achievable by a non-hybrid vehicle, such cars typically have very complex and expensive drive systems due to the use of two different drive technologies. Additionally, as hybrids still rely on an internal combustion engine for a portion of their power, the inherent limitations of the engine prevent such vehicles from achieving the levels of pollution emission control and fuel efficiency desired by many. Accordingly several car manufacturers are developing, and in some instances manufacturing, vehicles that utilize an all-electric drive system. The present invention provides an improved drive system for such a vehicle.